In recent mobile communication systems, not only line switching voice services, but also high-capacity packet switching multimedia services are being provided. The 3rd Generation Partnership Project has visualized MBMS user services, and released the associated UTRAN architectures and channel structures. (See below-listed Non-Patent Publication 1.) A base station supplies an MBMS notification indicator (NI) to mobile stations to encourage the mobile stations to subscribe to MBMS user services. Each of the mobile stations can select a desired service (for example, multicast news) from the received notification indicator (NI), and reports the selection to the base station. Then, a service subscription procedure is executed.
In this arrangement, the notification indicator (NI) is periodically transmitted using a physical channel named MBMS indicator channel (MICH) to those mobile stations not in CELL_DCH state, which means that dedicated channels have not been established between the base station and those mobile stations. The transmission interval or timing is designated by the logical channel called a MCCH. The mobile station that received the NI also receives the MCCH (logical channel) mapped to the secondary common control physical channel (SCCPCH) corresponding to the received MICH. The content of the MBMS is defined by a logical channel, such as MCCH, MTCH, or MSCH, as is known in the art.
On the other hand, a dedicated notification indicator (DNI) is transmitted on DCCH, which is a downlink logical channel, to those mobile stations in CELL_DCH state with dedicated channels already established. The DCCH is mapped to a dedicated physical channel DPCH. The mobile station receives the dedicated notification indicator (DNI) on this physical channel, and then receives MCCH, MTCH, or other logical channels.
In accordance to the procedure, the mobile station can appropriately receive the MBMS notification indicator (NI) in either state as long as it is located in the MBMS service area.
With the above-described technique, the minimum necessary radio channels that have to be received at the mobile station or user equipment (UE) are defined corresponding to each of the UE states, other than CELL_DCH state. This minimum ability required for the mobile station is called “Minimum UE Capability”.
To be more precise, the UE in CELL_PCH state or URA_PCH state has to have an ability to receive one PICH (physical channel) and one MICH (physical channel).
The UE in CELL_FACH state has to have an ability to receive one MICH (physical channel) and one SCCPCH (physical channel).
To the UE in CELL_PCH state, URA_PCH state, or IDLE state is periodically transmitted an MICH at a common transmission timing regardless of the radio resource control (RRC) state.
With the known method, the minimum UE capability is defined depending on the RRC state, and the radio channels that have to be received at the UE are determined in each of the states. Accordingly, the UE has to receive multiple radio channels simultaneously. This arrangement is undesired from the viewpoint of conserving battery power.
In addition, the types of radio channels received at the UE vary depending on the RRC states, and therefore, signal processing is likely to be complicated. For the mobile station in CELL_DCH state, a radio channel dedicated for a prescribed period of time may be used to transmit NI or other information. Concerning the mobile station in CELL_DCH state, the notification indicator (NI) or other information can be transmitted any time using a radio channel dedicated to that mobile station.
Meanwhile, in post-3G mobile communication systems, the data transmission scheme has been shifted from line switching to packet switching, and it is being studied and discussed how to transmit various logical channels using a single radio channel (e.g., an appropriately scheduled shared channel). Besides, the RRC states of UE are being simplified so as to be roughly classified into “ACTIVE” state and “IDLE” state, while CELL_FACH state is unlikely to be defined.
The “ACTIVE state” may then correspond to CELL_DCH state. It is being discussed to define “Dormant” as a sub-state of “ACTIVE”. “Dormant” may then correspond to CELL_PCH state.
If the number of RRC states of UE is actually decreased and the types of radio channels to be transmitted are decreased or simplified, then issues arising from the viewpoint of battery power savings and computational workload may be reduced.
Because of the characteristics of the MBMS notification indicator (NI) that are announced to all the users to encourage service subscription, it is desired for the MBMS NI to be transmitted to all the users at or above a certain frequency. The mobile station (UE) in the IDLE state or “Dormant” state is not communicating traffic data; instead, it is in the discontinuous-receive mode for receiving information from the base station intermittently. Accordingly, it may not be difficult to announce the MBMS notification indicator (NI) at intervals intended by the network.
However, in the ACTIVE state, transmission of traffic data does not necessarily occur periodically, and packet scheduling varies depending on various items including quantity of traffic and channel conditions. If under such circumstances a notification indicator (NI) is transmitted periodically to all the mobile station or user equipment in a single uniform way, thereby forcibly occupying a resource of the shared data channel at certain intervals, then efficient use of radio resources of the shared data channel will be prevented. Furthermore, the content of the notification indicator (NI) may not change frequently depending on the situation. In this case, the efficient use of radio resources is further degraded.                NON-PATENT PUBLICATION 1: 3GPP Interface Standard, 3GPP “TS25.211” and “TS25.346”        